Polyamines: Rising stars against metal and metalloid toxicity

Globally, metal/metalloid(s) soil contamination is a persistent issue that affects the atmosphere, soil, water and plant health in today's industrialised world. However, an overabundance of these transition ions promotes the excessive buildup of reactive oxygen species (ROS) and ion imbalance, which harms agricultural productivity. Plants employ several strategies to overcome their negative effects, including hyperaccumulation, tolerance, exclusion, and chelation with organic molecules. Polyamines (PAs) are the organic compounds that act as chelating agents and modulate various physiological, biochemical, and molecular processes under metal/metalloid(s) stress. Their catabolic products, including H₂O₂ and gamma amino butyric acid (GABA), are also crucial signalling molecules in abiotic stress situations, particularly under metal/metalloid(s) stress. In this review, we explained how PAs regulate genes and enzymes, particularly under metal/metalloid(s) stress with a specific focus on arsenic (As), boron (B), cadmium (Cd), chromium (Cr), and zinc (Zn). The PAs regulate various plant stress responses by crosstalking with other plant hormones, upregulating phytochelatin, and metallothionein synthesis, modulating stomatal closure and antioxidant capacity. This review presents valuable insights into how PAs use a variety of tactics to reduce the harmful effects of metal/metalloid(s) through multifaceted strategies.